Structural formula for ATP. The three phosphate groups are named alpha, beta and gamma from the ribose moiety. The nitrogen base (adenine) together with the sugar moiety (ribose) forms the molecule adenosine. If adenosine has only one phosphate group, it is called adenosine monophosphate (AMP). - Click on the image to enlarge it.
Adenosine triphosphate (ATP) is a nucleotide (nucleoside triphosphate) consisting of a nitrogen base (adenine), a sugar molecule (ribose) and a triphosphate group. ATP is the most important energy form for all organisms and can be said to be the cell's energy currency. The reason for this is that ATP contains energy-rich bonds between the phosphate groups and the chemical energy in these bonds can be recovered when such a group is cleaved from ATP and then ADP (adenosine diphosphate) is formed or from ADP to AMP (adenosine monophosphate). The cell cannot store ATP and the synthesis of ATP must constantly be regulated in relation to the need. ATP is also a building block for synthesis of nucleic acid.
Energy is required for the synthesis of ATP from ADP and phosphate. That energy can be generated by glycolysis, during the Krebs cycle and through the electron transport chain. Some intracellular bacteria (e.g. members of the Chlamydiaceae family) cannot synthesize the amount of ATP required for the various functions of the cell and must, therefore, parasitize on the host cell's ATP synthesis.
The energy-demanding processes, which utilize ATP, can in bacterial cells be divided into three main groups:
The German-British biochemist Hans Krebs was awarded the Nobel Prize in physiology or medicine in 1953 for investigating and presenting the most important parts of the citric acid cycle in the 1930s.